Added working demo for hierarchical coref.
- implementation of CollapsedParseTree
- new ParseTree structure (see trait ParseTree2); which can be created from current ParseTree implementation, and has nearly the same functionality and structure
- introduction of mutable and and immutable parse trees for the new structure, for efficient implementation of several functions
- bug fix- label,vertex,parent-Arrays were initialized later than variables that depend on them
- simple test class for CollapsedParseTree (has to be extended some day)
- CollapsedParseTree toString works
- fix for collapsing also phrases
- fix for collapsing prepositions
- better toString by including all tokens of a phrase instead of just the head
working through issues.
bug fix: filter instead of takeWhile of course
adding as to parse tree label domain as a possible preposition
fixes preposition collapsing for special cases like "such as", in which the preposition has modifiers (don't collapse)
simple performance improvements when collapsing parse trees
handling nested phrases
filter mentions of that are not part of the sentence to be collapsed
bug fix
Merge branches 'master' and 'master' of https://github.com/factorie/factorie
Performing to spec with LegacyPairGenerator.

!!! FOR REALS !!!
Removed trace file.
Cleaning up move generators and removing commented code.
Renamed context generator and added support for early stopping.
Added code to automatically stop sampling when appropriate.
Merge branch 'sri-coref'